LTC1733EMSE#TR Linear Technology, LTC1733EMSE#TR Datasheet - Page 13

• Manufacturer Part Number: LTC1733EMSE#TR
• Description: IC CTRLR BATT CHRG LI-ION 10MSOP
• Manufacturer: Linear Technology

Specifications of LTC1733EMSE#TR

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.5 V ~ 6.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width) Exposed Pad
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in the
Programming Charge Current section.
It is important to remember that LTC1733 applications do
not need to be designed for worst-case thermal conditions
since the IC will automatically reduce power dissipation
when the junction temperature reaches approximately
105 C. See Design Note 283 for additional information.
Board Layout Considerations
In order to be able to deliver maximum charge current
under all conditions, it is critical that the exposed pad on
the backside of the LTC1733 package is soldered to the
board. Correctly soldered to a 2500mm
1oz. copper board the LTC1733 has a thermal resistance
of approximately 40 C/W. Failure to make thermal contact
between the exposed pad on the backside of the package
and the copper board will result in thermal resistances far
greater than 40 C/W. As an example, a correctly soldered
LTC1733 can deliver over 1250mA to a battery from a 5V
supply at room temperature. Without a backside thermal
connection, this number could drop to less than 500mA.
V
Many types of capacitors can be used for input bypassing.
However, caution must be exercised when using multi-
layer ceramic capacitors. Because of the self resonant and
high Q characteristics of some types of ceramic capaci-
tors, high voltage transients can be generated under some
start-up conditions, such as connecting the charger input
to a hot power source. For more information refer to
Application Note 88.
CC
I
BAT
Bypass Capacitor
(
5
V
– .
105
3 75
U
C
V
–
)•
55
40
U
C
C W
/
W
50
50
C A
2
C
/
double-sided
U
1
A
Stability
The constant-voltage mode feedback loop is stable
without any compensation when a battery is connected.
However, a 1 F capacitor with a 1 series resistor to GND
is recommended at the BAT pin to keep ripple voltage low
when the battery is disconnected.
In the constant-current mode it is the PROG pin that is in
the feedback loop and not the battery. The constant-
current mode stability is affected by the impedance at the
PROG pin. With no additional capacitance on the PROG
pin, stability is acceptable with program resistor values as
high as 50k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 500kHz.
Therefore, if the PROG pin is loaded with a capacitance, C,
the following equation should be used to calculate the
maximum resistance value for R
Average, rather than instantaneous, battery current may
be of interest to the user. For example, if a switching power
supply operating in low-current mode is connected in
parallel with the battery the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
battery current as shown in Figure 4. A 10k resistor is
added between the PROG pin and the filter capacitor and
monitoring circuit to ensure stability.
Figure 4. Isolating Capacitive Load on PROG Pin and Filtering.
R
PROG
< 1/(6.283 • 500E3 • C)
LTC1733
GND
PROG
5
7
R
PROG
C
10k
FILTER
PROG
1733 F04
:
LTC1733
CHARGE
CURRENT
MONITOR
CIRCUITRY
sn1733 1733fs
13